U.S. patent number 4,374,350 [Application Number 06/216,836] was granted by the patent office on 1983-02-15 for control system for stopping spindle at predetermined rotational position.
This patent grant is currently assigned to Fujitsu Fanuc Limited. Invention is credited to Yoshiki Fujioka, Yoshinori Kohzai, Naoto Ota.
United States Patent |
4,374,350 |
Kohzai , et al. |
February 15, 1983 |
**Please see images for:
( Certificate of Correction ) ** |
Control system for stopping spindle at predetermined rotational
position
Abstract
A system employed in a machine tool of the type in which a gear
mechanism disposed between the spindle and spindle motor transmits
the rotational motion of the motor to the spindle. The system
allows the spindle to be brought to a stop at a predetermined
rotational position in a shorter period of time when the gear
mechanism is set in low gear, that is, while the rotational speed
of the motor is being reduced by the gear mechanism as it is being
transferred to the spindle. This permits the spindle to be stopped
at the predetermined position in the same amount of time which is
required when no reduction in speed takes place between the motor
and spindle. When the spindle arrives at a region where it is to be
controlled in order to stop at the predetermined rotational
position, a position deviation signal for guiding the spindle to
the position is applied as an input signal to a speed control loop
for controlling spindle rotation. The position deviation signal
varies in dependence upon the gear ratio of the spindle gear
mechanism. Positioning gain, which is obtained by dividing the
speed of the spindle motor by an amount of spindle motor rotation
that depends upon the position deviation of the spindle; is
controlled so that it remains constant regardless of the speed
change ratio between the spindle and spindle motor as determined by
the gear mechanism.
Inventors: |
Kohzai; Yoshinori (Hino,
JP), Fujioka; Yoshiki (Hino, JP), Ota;
Naoto (Hino, JP) |
Assignee: |
Fujitsu Fanuc Limited (Tokyo,
JP)
|
Family
ID: |
15946384 |
Appl.
No.: |
06/216,836 |
Filed: |
December 15, 1980 |
Foreign Application Priority Data
|
|
|
|
|
Dec 31, 1979 [JP] |
|
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54-172681 |
|
Current U.S.
Class: |
318/590;
318/616 |
Current CPC
Class: |
G05B
19/39 (20130101); G05B 2219/49273 (20130101); G05B
2219/41358 (20130101); G05B 2219/41021 (20130101) |
Current International
Class: |
G05B
19/39 (20060101); G05B 19/19 (20060101); G05B
011/18 () |
Field of
Search: |
;318/590,616,591,615,561 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dobeck; B.
Attorney, Agent or Firm: Staas & Halsey
Claims
What we claim is:
1. A control system for stopping a spindle at a predetermined
rotational position, for driving a spindle with a spindle motor
through a speed change mechanism, having a speed change ratio, in
such a manner that a positional deviation between a present
rotational position of a specified point on the spindle and the
predetermined rotational position at which the specified point is
to be stopped, is reduced to zero, thereby stopping the specified
point on the spindle at the predetermined rotational position, said
control system comprising means, operatively connected to the
spindle and to the spindle motor, for generating a positioning gain
by dividing the speed of the spindle motor by an amount of spindle
motor rotation which depends upon the positional deviation of the
spindle, said positioning gain being generated so as to remain
substantially constant regardless of the speed change ratio
established between the spindle motor and the spindle by said speed
change mechanism, thereby stopping the specified point on the
spindle at the predetermined rotational position.
2. A control system according to claim 1, wherein said means for
generating said positioning gain generates said positioning gain by
dividing the speed of the spindle motor, one revolution before the
specified point on the spindle reaches the predetermined rotational
position, by an amount of spindle motor rotation required for one
revolution of the spindle, and said positioning gain is so
generated as to remain substantially constant.
3. A control system according to claim 1 or 2, wherein said control
system has a spindle stopping control mode, wherein said means for
generating said positioning gain generates said positioning gain
that is finely adjustable during the spindle stopping control
mode.
4. A control system, operatively connectable to receive an
orientation command signal, for stopping a spindle at a
predetermined rotational position, and for driving a spindle
through a speed change mechanism, so that a specified point on the
spindle is stopped at the predetermined rotational position, said
control system comprising:
actual speed means for generating an actual speed signal;
a speed command circuit for generating a speed command signal;
means, coupled to the spindle, for detecting the rotation of the
spindle and for generating a deviation signal and an approach
signal;
an orientation control circuit, having a first input operatively
connected to said detecting means, having a second input
operatively connected to said actual speed means and having a third
input operatively connectable to receive the orientation command
signal, for generating a rotational position deviation signal, an
orientation completion signal and a loop changeover signal; and
a loop changeover switch, having a first switchable terminal
operatively connected to said orientation control circuit and
having a second switchable terminal operatively connected said
speed command circuit, for outputting the speed command signal or
the rotational position deviation signal in dependence upon the
loop changeover signal.
5. A control system according to claim 4, wherein said orientation
control circuit is operatively connectable to receive high and low
gear signals, wherein said spindle rotates in a forward and a
reverse direction, wherein said means for detecting the rotation of
the spindle includes a magnetic body mounted on the spindle and a
sensor positioned opposite the magnetic body and having a gap
therebetween, wherein said orientation control circuit
comprises:
a gain adjustment circuit, operatively connected to said detecting
means, for receiving the deviation signal, for adjusting the gain
in dependence upon the gap between the magnetic body and the sensor
and for generating a fine position deviation signal;
a slicer circuit, operatively connected to said detecting means,
for slicing the approach signal at a predetermined level and for
generating an a first switching signal which indicates that the
magnetic body has reached a predetermined point near the
predetermined rotational position;
means, operatively connected to said gain adjustment circuit, for
generating an in-position signal when the fine position deviation
signal is within a predetermined range;
a first comparator, operatively connected said gain adjustment
circuit, for comparing the fine position deviation signal with a
direction reference signal and for generating a reverse signal when
the spindle is approaching the predetermined rotational position
while rotating in the reverse direction;
a second comparator, operatively connected said gain adjustment
circuit, for comparing the fine position deviation signal with the
direction reference signal and for generating a forward signal when
the spindle is approaching the predetermined rotational position
while rotating in the forward direction;
a first changeover circuit, operatively connected to said actual
speed means and operatively connectable to receive the low and high
gear signals, for switching the gain applied to the actual speed
signal in dependence upon the low gear and high gear signals;
signal means, operatively connected to said first changeover
circuit, for generating an initially set voltage signal, a bias
signal and a coarse deviation signal, for integrating the actual
speed signal received from said first changeover circuit and for
substracting the result of the integration from the initially set
voltage signal;
an absolute value circuit, operatively connected to said signal
means, for receiving the initially set voltage signal, the coarse
position deviation signal and the bias signal, and for generating
an absolute value signal;
a third comparator circuit, operatively connected to said absolute
value circuit, for comparing the absolute value signal with a
predetermined signal and for generating a second switching signal
when the absolute value signal is less than the predetermined
signal;
a forward reverse changeover circuit, having first and second
inputs operatively connected to said absolute value circuit and
having first and second outputs, for generating an amplified
absolute value signal or for passing therethrough the absolute
value signal in dependence upon the direction of rotation of the
spindle;
a switch, operatively connected to said gain adjustment circuit and
to said slicer circuit, for passing therethrough the fine position
deviation signal in dependence upon the first switching signal;
a second changeover circuit, having a first input operatively
connected to said switch, having second and third inputs
operatively connected to said forward reverse changeover circuit
and having an output operatively connected to said loop changeover
circuit, for receiving the fine position deviation signal, for
receiving the amplified absolute value signal, for receiving the
absolute value signal and for generating the rotational position
deviation signal;
a speed detection circuit, operatively connected to said actual
speed means and operatively connectable to receive the high and low
gear signals, for generating a predetermined speed signal
indicating that the spindle has reached a predetermined speed and
for generating a zero speed signal when the spindle stops
rotating;
a loop changeover circuit, operatively connected to said speed
detection circuit, to said loop changeover switch and operatively
connectable to receive the orientation command signal, for
generating the loop changeover signal when the predetermined speed
signal and the orientation command signal are present; and
an orientation completion signal generating circuit, operatively
connected to said speed detection circuit, to said means for
generating the in-position signal and operatively connectable to
receive the orientation command signal, for generating the
orientation completion signal when the zero speed signal, the
orientation command signal, and the in-position signal are
present.
6. A control system according to claim 5, wherein said first
changeover circuit comprises:
a variable resistor, having a first terminal operatively connected
to said actual speed means, having a second terminal operatively
connected to ground and having a third terminal for outputting a
modified actual speed signal;
a first switch, operatively connected to said actual speed means,
to said signal means and operatively connectable to receive the low
gear signal, for passing the actual speed signal therethrough when
the low gear signal is received; and
a second switch, operatively connected between the third terminal
of said variable resistor and said signal means and operatively
connectable to receive the high gear signal, for passing
therethrough the modified actual speed signal when the high gear
signal is received.
7. A control system according to claim 5, wherein said signal means
comprises:
a changeover switch, having first and second switchable terminals
operatively connected to first and second reference voltages,
respectively, for switching between the first and second reference
voltages in dependence upon the direction of rotation of the
spindle;
a first resistor having a first terminal operatively connected to
said changeover switch and having a second terminal;
a first amplifier having a first input operatively connected to the
second terminal of said first resistor, having a second input and
having an output;
a second resistor having a first terminal operatively connected to
the output of said first amplifier and having a second
terminal;
a first switch, operatively connected to said third comparator,
having a switchable terminal operatively connected to the second
terminal of said second resistor and having a nonswitchable
terminal, said first switch closing when the second switching
signal is received;
an integration circuit, having a first input operatively connected
to the nonswitchable terminal of said first switch, having a second
input operatively connected to said first changeover circuit and
having an output operatively connected to the second input of said
first amplifier and to said absolute value circuit, for generating
the initially set voltage, the coarse position deviation signal and
the bias signal;
a third resistor having a first terminal operatively connected to
the output of said integration circuit and having a second
terminal; and
a second switch, operatively connected to said third comparator and
operatively connected between the second terminal of said third
resistor and the first input of said integration circuit, said
second switch closing when the second switching signal is
received.
8. A control system according to claim 7, wherein said signal means
further comprises a fourth resistor operatively connected between
the second terminal of said first resistor and ground.
9. A control system according to claim 7, wherein said integration
circuit comprises:
a variable resistor having a first terminal operatively connected
to said first changeover circuit and having a second terminal;
a second amplifier, having a negative input operatively connected
to both the second terminal of said variable resistor and the
nonswitchable terminal of said first switch and having an output
operatively connected to said absolute value circuit, for
generating the initially set voltage signal, the bias signal and
the coarse deviation signal; and
a capacitor operatively connected between the negative input and
the output of said second amplifier.
10. A control system according to claim 9, wherein said second
amplifier has a positive input, wherein said integration circuit
further comprises a resistor operatively connected between the
positive input and ground.
11. A control system according to claim 5, wherein said
forward-reverse changeover circuit comprises:
an amplifier, operatively connected to said absolute value circuit
and to said second changeover circuit, for generating the amplified
absolute value signal;
a first forward reverse switch, operatively connected to said
amplifier, to said second changeover circuit, to said speed
detection circuit, to said first comparator and to said slicer
circuit, for passing therethrough the amplified absolute value
signal in dependence upon the predetermined speed signal, the
reverse signal, the forward signal and the first switching signal;
and
a second forward reverse switch, operatively connected to said
second changeover circuit, to said absolute value circuit to said
speed detection circuit, to said first comparator and to said
slicer circuit, for passing therethrough the absolute value signal
in dependence upon the predetermined speed signal, the reverse
signal, the forward signal and the first switching signal.
12. A control system according to claim 5, wherein said second
changeover circuit comprises:
first and second means for generating first and second correction
signals, respectively;
an adder circuit, having a first input operatively connected to
said switch, having second and third inputs operatively connected
to said forward-reverse changeover circuit, having a fourth input
operatively connected said means for generating the first
correction signal and having an output, for adding the first
correction signal to the fine position deviation signal, to the
amplified absolute value signal or to the absolute value signal in
dependence upon which signal is received, and for generating an
adder signal; and
means, operatively connected to the output of said adder and
operatively connected to said second means for generating the
second correction signal, to said loop changeover switch and
operatively connectable to receive the high and low gear signals,
for dividing the adder signal, for adjusting a dividing ratio, for
adjusting gain in dependence upon the high or low gear signals, for
modifying the adder signal in dependence upon the second correction
signal and for generating the rotational position deviation
signal.
13. A control system as recited in claim 12, wherein said adder
circuit comprises:
first through third resistors, each having a first terminal
operatively connected to said switch and to said forward reverse
changeover circuit, respectively, and each having a second
terminal;
an amplifier having a first input operatively connected to the
second terminal of said first through third resistors, having a
second input and having an output operatively connected to said
driver means;
a variable resistor having a first terminal operatively connected
between the first input and the output of said amplifier and having
a second terminal; and
fourth and fifth resistors operatively connected in series between
the second input of said amplifier and ground, a connection point
formed between said fifth and sixth resistors operatively connected
to said first means for generating the first correction signal.
14. A control system according to claim 12, wherein said first and
second means for generating the first and second correction signals
each comprise a variable resistor having a first input operatively
connected to a first reference voltage, having a second input
operatively connected to a second reference voltage and having an
output.
15. A control system according to claim 12, wherein said means for
dividing the adder signal, for adjusting the dividing ratio, for
adjusting the gain and for modifying the adder signal in dependence
upon the second correction signal comprises:
a first resistor having a first terminal operatively connected to
the output of said adder circuit and having a second terminal;
a variable resistor having a first terminal operatively connected
to the second terminal of said first resistor, having a second
terminal and having a third terminal;
a second resistor operatively connected between the second terminal
of said variable resistor and ground;
a first switch, operatively connectable to receive the low gear
signal, having a first terminal operatively connected to the output
of said adder circuit and having a second terminal operatively
connected to said loop changeover switch, for outputting the
rotational position deviation signal, wherein said first switch
closing in dependence upon the low gear signal; and
a second switch, operatively connectable to receive the high gear
signal, having a first terminal operatively connected to the third
terminal of said variable resistor and to said second means for
generating a second correction signal and having a second terminal
operatively connected to said loop changeover circuit, for
outputting the rotational position deviation signal, wherein said
second switch closing in dependence upon the high gear signal.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is related to the following applications:
(1) U.S. Application Ser. No. 216,835 by Kohzai et al. entitled
"Control System for Stopping Spindle at Predetermined Rotational
Position"; and
(2) U.S. Application Ser. No. 216,837 by Kohzai et al. entitled
"Control System of Stopping Spindle at Predetermined Rotational
Position"; both of the above applications are assigned to the
assignee of the present application.
BACKGROUND OF THE INVENTION
This invention relates to a control system for stopping a spindle
at a predetermined rotational position, and more particularly to a
control system of the type described, which permits the control
operation to be performed in a short period of time by rendering
the positioning gain approximately constant regardless of the speed
change ratio, between the spindle and a motor, as determined by a
speed change mechanism.
In an automatic tool change mechanism of a machine tool, a key is
provided on the spindle of the machine tool and a keyway is formed
in each of the various tools that are employed. In order to mate
the spindle and tool with each other smoothly, the spindle must be
positioned and stopped accurately in such a manner as to bring the
key and keyway into perfect alignment. There is a similar
requirement in machine tools for cutting work, and for boring work
in particular. Here it is desirable to employ a boring bar having a
large diameter in order to eliminate chatter, and to stop a
specified point on the spindle at a predetermined rotational
position in an accurate manner in order that the cutting operation
may proceed in a stable and rigid fashion.
Mechanical stopping mechanisms that rely upon a pin or brake are
generally employed to stop the spindle at the predetermined
position. However, such mechanisms experience wear with long use,
particularly of the pin and brake shoe portions, so that it becomes
progressively more difficult to stop the spindle at the correct
position. These mechanisms also require troublesome maintenance and
inspections.
Accordingly, the assignee of present invention has already proposed
a system, disclosed in copending U.S. applications by Kohzai et al.
with Ser. No. 190,659 entitled "Spindle Rotation Control System"
and by Fujioka with Ser. No. 215,631 entitled "Control System for
Stopping Spindle at Predetermined Rotational Position" both
assigned to the assignee of the present application, for stopping a
specified point on spindle at a predetermined rotational position
through purely electrical means without relying upon a mechanical
brake or the like. Although the already proposed system succeeds in
stopping the spindle with a high degree of accuracy, a considerable
amount of time may be required to accomplish the stopping if the
speed change ratio between the spindle and the spindle driving
motor is high. This naturally results in a poorer working
efficiency.
Approximately 90% of the machine tools of the ordinary variety
employ a speed change mechanism, such as a gear mechanism between
the motor and spindle, so that machining can be performed while
switching between a high gear setting (reduction ratio low) and a
low gear setting (reduction ratio high). The high gear setting is
used for the light machining of wood or light metals such as
aluminum, whereas the low gear setting is employed for the heavy
machining of steel or the like.
In the already proposed control system for stopping a spindle at a
predetermined rotational position, the control mode for stopping
the spindle begins after the generation of a single for one spindle
revolution, with the specified point on the spindle being stopped
correctly at the predetermined position after the one revolution.
To accomplish this the gear ratio between the spindle and motor is
set to high gear (1:1) to enable the spindle to be stopped after a
single revolution of the motor. In the low gear setting, however,
where the motor-to-spindle ratio is typically 4:1, four revolutions
of the motor are required to bring the spindle to a stop. Thus the
time required for the stopping operation in low gear is at least
four times that of high gear, so that the proportion of time spent
for actual machining work decreases. The inevitable result is a
decline in working efficiency.
In general, with the high gear setting in which the gear ratio is
1:1, load inertia increases and speed loop gain decreases, while
the opposite is true in the low gear setting in which the gear
ratio is 4:1, as mentioned above. In other words, when applying the
orientation control operation to stop the spindle at the
predetermined position, the low gear setting allows the motor speed
to be increased in comparison with the speed under a high gear
setting.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a
control system which permits a spindle to be stopped at a
predetermined rotational position in a shorter period of time even
if the speed change ratio is high in a machine tool of the type in
which the rotational speed of a spindle motor is changed through a
speed change mechanism before being transmitted to the spindle.
It is another object of the present invention to provide a control
system which permits a spindle to be stopped at a predetermined
rotational position within a fixed period of time, regardless of
the speed change ratio, by allowing positioning gain, which is
obtained by dividing the rotational speed of the spindle motor by a
residual amount of spindle motor rotation, to be set to a
substantially constant value regardless of the speed change
ratio.
It is a further object of the present invention to provide a
control system which permits a spindle to be stopped at a
predetermined rotational position without overshooting the
predetermined rotational position even when the positioning gain is
varied in accordance with the speed change ratio.
Other features and advantages of this invention will be apparent
from the following description taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(a) and 1(b) are illustrative views which are useful in
describing positioning gain as well as the principle of the present
invention;
FIG. 2 is a circuit block diagram of a control apparatus for
stopping a spindle at a predetermined rotational position, and
which embodies the system of the present invention;
FIGS. 3(a) and 3(b) are illustrative views showing the arrangement
of a position sensor, and FIG. 3(c) is a waveform diagram of output
signals associated therewith;
FIGS. 4(a) and 4(b) are illustrative views showing the internal
structure of the position sensor of FIG. 3, and FIG. 4(c) is a
waveform diagram of output signals associated therewith;
FIG. 5 is a circuit diagram of a portion of the position sensor of
FIG. 3;
FIGS. 6(a), 6(c) and 6(d) are B-H graphs and 6(b) is an are
illustrative view which are useful in describing the operation of
the position sensor;
FIGS. 7(a) and 7(b) are waveform diagrams associated with the
control system of the present invention;
FIG. 8 is a detailed circuit diagram of a principal portion of a
rotational position deviation signal generating circuit;
FIG. 9 is a waveform diagram of signals associated with the
rotational position deviation signal generating circuit of FIG. 8;
and
FIG. 10 is an illustrative view which is useful in describing the
relationship between positioning gain and overshoot.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference will first be had to FIG. 1 to describe positioning gain
as well as the principle of the present invention. FIGS. 1(a) and
1(b) are illustrative views of high and low gear situations,
respectively.
FIG. 1(a) shows that, when in a high hear setting, a spindle is
rotating at a predetermined speed until a time t.sub.1 since the
particular machine tool is performing cutting work or the like up
to this time. When an orientation command is issued at time
t.sub.1, the rotational speed of the spindle is reduced and reaches
a preset speed V.sub.H at time t.sub.2. The spindle rotates at this
speed until the generation of a signal for one spindle revolution,
as will be described later. If this signal is generated at time
t.sub.3, a spindle control operation for stopping the spindle
begins at this point and continues until, at time t.sub.4, a
specified point on the spindle is stopped at the predetermined
position.
On the other hand, in FIG. 1(b) which shows the conditions for
operation in low gear, the rotational speed of the spindle is
reduced and reaches a preset speed V.sub.L at time t.sub.2 '
following the issuance of the orientation command at time t.sub.1.
The spindle rotates at the preset speed until the generation of the
signal for one spindle revolution. If the signal for one spindle
revolution is generated at time t.sub.3 ', a spindle control
operation for stopping the spindle begins at this point and
continues until, at time t.sub.4 ', a specified point on the
spindle is stopped at the predetermined position.
If the set speed V.sub.H, while in high gear, and the set speed
V.sub.L, while in low gear, are equal, then, because the gear ratio
is 1:1 in high gear and 4:1 in low gear, the period of time from
the generation of the one revolution signal until the completion of
the spindle stopping control operation will be at least four times
longer in low gear than in high gear. Accordingly, if the value of
V.sub.L is set to be four times that of V.sub.H, it may be presumed
that the time required to stop the spindle in low gear will be
equal to that required to accomplish the same in high gear. This
means that in order to make the positioning gain in high gear the
same as that in low gear requires that the positioning gain during
the spindle stopping control operation be defined as V/.theta..
Where V represents the speed of the motor in radians per second,
and .theta., also measured in radians, represents the amount
through which the spindle motor rotates until a positional
deviation, between a specified point on the spindle and a
predetermined rotational position, is reduced to zero. The
positional deviation mentioned here arises when the motor, which
has been rotating at a constant speed, is instructed to decrease
the speed in order to stop the spindle. The motor is then driven so
as to reduce the positional deviation to zero. Thus, the
positioning gain V/.theta. is generally represented by dividing a
command speed by a positional deviation which is measured from a
predetermined stopping position. If we let n.sub.H represent the
number of motor revolutions needed to revolve the spindle once in
high gear, and let n.sub.L represent the number of motor
revolutions needed to revolve the spindle once in low gear, then
the positioning gain PG(H) for high gear and the positioning gain
PG(L) for low gear, at the time of a control operation for stopping
the spindle at the predetermined rotational position, with be
expressed by the following:
In order to set the value of V.sub.L equal to a value which is, for
example, four times that of V.sub.H, an arrangement in accordance
with the present invention is constructed so adapted that the gain
of the positioning control system can be changed in both high and
low gear when the spindle is being subjected to positioning control
to stop it at the predetermined position.
Next, reference will be had to FIG. 2 which shows a block diagram
of a spindle control apparatus to which the present invention may
be applied. There are included a speed command circuit 1 for
generating a speed command CV, and an orientation command circuit 2
for generating an orientation command ORCM. A speed control circuit
3 includes an adder 3a, a phase compensating circuit 3b connected
to the output of the adder, a voltage-to-phase converter 3c
connected to the output of the phase compensating circuit, and a
thyristor converter 3d connected to the output of the converter 3c.
The adder 3a is constructed so that it generates both (1) a
difference voltage, representative of a speed deviation, which is
the difference between the voltage of the speed command CV and the
voltage of an actual speed signal, during a speed control
operation, and (2) and generates a difference voltage between a
rotational position deviation RPD and the actual speed AV. The
phase compensating circuit 3b subjects the output voltage of the
adder 3 to a phase compensation by advancing or retarding the phase
of the output of the adder 3a. The voltage-to-phase converter 3c
controls the firing angle of each thyristor in the thyristor
circuit 3d in dependence upon the output voltage of the phase
compensating circuit 3b. The thyristor converter 3d operates, in
dependence upon the controlled firing angles of its thyristors, to
convert the three-phase voltage from a three-phase power supply 3e
into a direct current. The direct current is used to vary the value
of the voltage applied to a DC motor which will be described later,
thereby regulating the speed at which the motor rotates. The DC
motor 4 serves as a spindle drive motor. As the DC motor 4 rotates,
a tachometer generator 5 generates a voltage in dependence upon the
motor speed. The rotational motion of the DC motor 4 is transmitted
through a gear mechanism 9 to a spindle 7. The gear mechanism 9 is
capable of being changed between high and low gear by means of an
externally applied changeover signal. The spindle 7 is coupled to a
spindle mechanism 6 which holds a tool 8. A rotational position
sensor 10 is constructed so that it will detect the rotational
position of the spindle 7 and comprises a magnetic body 10a which
is attached to the spindle 7, a sensing portion 10b which is
attached to a stationary portion of the machine such as the spindle
bearing portion, for sensing the magnetic body 10a, and an
electrical circuit 10c, as shown in FIGS. 3a and 3b. the position
sensor 10 generates a fine position deviation signal DV.sub.2 and
an approach signal ASV, shown in FIG. 3c, which vary in dependence
upon the rotational deviation of the spindle 7 with respect to a
predetermined rotational position OS at which a specified point on
the spindle is to be stopped.
Referring again to FIG. 2, an orientation control circuit 11
includes a rotational position deviation signal generating circuit
11a which receives the fine position deviation signal DV.sub.2, the
approach signal ASV, and the signal AV, indicative of the actual
speed of the spindle, provided by the tachometer 5. The rotational
position deviation signal generating circuit 11a generates the
rotational position deviation signal RPD which serves as a spindle
speed command signal when an operation which is for stopping the
spindle at the predetermined rotational position is being carried
out. The rotational position deviation signal generating circuit
11a also generates an orientation completion signal ORDEN and a
signal VSR indicating that the prescribed speed has been reached.
The orientation control circuit 11 also includes also a loop
changeover circuit 11b for actuating a loop changeover switch 12 in
dependence upon both the orientation command signal ORCM output by
the orientation command circuit 2 and the signal VSR output by the
position deviation signal generating circuit 11a.
Reference will now be made to FIGS. 3(a) and 3(b) for a complete
understanding of the structure and operation of the position sensor
10, FIG. 3(a) showing a front view and FIG. 3(b) a plan view of an
example in which the magnetic body 10a is mounted on the spindle 7.
It should be noted that the sizes of the magnetic body 10a and
sensing portion 10b are exaggerated in comparison with the size of
the spindle 7. The magnetic body 10a is mounted on the spindle 7 so
that the center of the magnetic body 10a will coincide with the
center of the sensing portion 10b when a specified point on the
spindle is located at the predetermined rotational position at
which the spindle is desired to be stopped. As the spindle 7
rotates the electrical circuit 10c generates the fine position
deviation signal DV.sub.2 and the approach signal ASV having the
waveforms shown in FIG. 3(c). The magnetic body 10a, as shown in
FIG. 4(a), has magnets 10a", 10a"', possessed of a triangular
cross-section, mounted in a case 10a' in such a manner that the
intensity of the magnetic field changes from S to N in the
direction of spindle rotation, i.e., in the direction of the arrow.
The sensing portion 10b is mounted on a mechanically stationary
portion of the machine so as to confront the magnetic body 10a, and
includes three saturable reactors SRA.sub.1, SRA.sub.2 and
SRA.sub.3 included in a case 10b' and aligned in the direction of
spindle rotation, as shown in FIG. 4(a). Each of the saturable
reactors comprises coils L.sub.1 and L.sub.2 wound on a core CR, as
shown in FIG. 4(b). The coils L.sub.1 and L.sub.2 on each core have
the same number of turns and are wound in opposite directions. The
coils on each core share a common terminal TA to which a
high-frequency signal is applied, and signals which are dependent
upon with the rotational position of the magnetic body 10a are
obtained at the terminals TB and TC of the respective coils.
Included in the electrical circuit 10c is a circuit shown in FIG.
5, associated with a corresponding one of the saturable reactors
SRA for processing the signal generated by the respective reactor.
Included in the electrical circuit 10c are a pulse oscillator OSC
for generating a 100 kHz high-frequency signal, an isolating
transformer ITR, and half-wave rectifiers HWR.sub.1 and HWR.sub.2.
The saturable reactor SRA is excited by the high-frequency pulse
signal HFP through the intermediary of the isolating transformer
ITR. As a result, an analog output voltage is obtained across the
terminals a and b of the circuit, which analog output voltage is
proportional to the external magnetic field H.sub.ext. The external
magnetic field strength varies in dependence upon the rotational
position of the magnetic body 10a.
Next, referring to FIG. 6, the action of the analog output voltage
which is generated between the terminals a and b and which depends
upon the rotational deviation of the spindle 7 will be described in
connection with the centrally located reactor SRA.sub.2 shown in
FIG. 4(a). When the magnetic body 10a is remote from the saturable
reactor SRA.sub.2 so that the external magnetic field acting upon
the reactor has a value approaching zero, the high-frequency pulse
signal HFP acts about the vertical zero line of the reactor B-H
curve, as shown in FIG. 9(a). In other words, the number of lines
of flux cutting the coils L.sub.1 and L.sub.2 are equal, so that
the output voltages from the terminals TB and TC are equal in
amplitude but displaced in phase by 180 degrees. It should be noted
that the core forming each saturable reactor SRA.sub.2 has a
hysteresis characteristic which is so small as to be negligible.
Since the voltages from the terminals TB and TC are rectified by
the respective half-wave rectifiers HWR.sub.1 and HWR.sub.2, the
potentials at the terminals a and b are equal, so that the voltage
across a and b is zero. Now, as the spindle 7 rotates and the
magnetic body 10a approaches the centrally located saturable
reactor SRA.sub.2, the external magnetic field H.sub.ext being
generated by the magnetic body begins to act upon the saturable
reactor SRA.sub.2. If we let h.sub.l denote the field generated by
the high-frequency pulse signal HFP, a flux of h.sub.l -H.sub.ext
will cut the coil L.sub.1, as shown in FIG. 6B, and a flux of
h.sub.l +H.sub.ext will cut the coil L.sub.2. If this is expressed
using a B-H curve, the high-frequency pulse signal HFP will act
about the line -H.sub.ext with respect to the coil L.sub.1, as
shown in FIG. 6(c), and about the line +H.sub.ext with respect to
the coil L.sub.2, as depicted in FIG. 6(d). Therefore, the
negatively directed flux which cuts the coil L.sub.1 causes
saturation of the core so that there is a smaller amount of
amplitude variation, whereas the negatively directed flux which
crosses the coil L.sub.2 does not cause saturation so that there is
a greater amount of amplitude variation. In view of the fact that
the induced voltage e takes on the value (-Nd.phi./dt) (where N is
the number of turns), the potential at the terminal b will become
greater than the potential at terminal a, giving rise to a
potential difference between the terminals. This potential
difference will vary in the manner of the fine position deviation
signal DV.sub.2 shown in FIG. 4(c) and, as the magnetic body 10a
continues to rotate, will become zero when the center of the
magnetic body 10a coincides with the center line of the saturable
reactor SRA.sub.2. The result is an analog voltage signal having
maximum and minimum values. Similarly, the saturable reactors
SRA.sub.1 and SRA.sub.3 on the left and right sides of the sensing
portion 10b, respectively, and the two half-wave rectifiers
associated with each reactor, cooperate to generate a potential
difference across the terminals a, b of each corresponding circuit.
This potential difference also defines an analog voltage signal and
similar to that of the fine position deviation signal DV.sub.2,
having maximum and minimum values. Thus, the analog voltage signals
associated with the reactors SRA.sub.1 and SRA.sub.3 also depend
upon the rotation of the magnetic body 10a on the spindle 7.
The electrical circuit 10c of the position sensor 10 further
includes a conversion circuit for generating a signal DV.sub.3,
shown in FIG. 4(c), by subjecting to a 180-degree phase conversion
the analog voltage signal which is generated by the saturable
reactor SRA.sub.3 and which varies in dependence upon the
rotational movement of the magnetic body 10a. The electrical
circuit 10c also includes a circuit which generates the approach
signal ASV, also shown in FIG. 4(c), by adding together the signal
DV.sub.3 and the analog voltage signal, denoted by DV.sub.1, which
is generated by the saturable reactor SRA.sub.1 and which varies in
dependence upon the rotational movement of the magnetic body 10a.
The approach signal ASV indicates that a specified point on the
spindle 7 has reached a point in the environs of the predetermined
rotational position.
The operation of the rotational position deviation signal
generating circuit 11a will now be described with reference to
FIGS. 2 and 7(a).
The rotational position deviation signal generating circuit 11a,
shown in FIG. 2, receives the fine position deviation signal
DV.sub.2, the approach signal ASV output by the position sensor 10
and the actual speed signal AV output by the tachometer 5. The
actual speed signal AV is integrated within the circuit 11a, and
the output signal resulting from the integration operation is
subtracted from a yet to be described initially set voltage ISV
(-V.sub.i when the spindle is rotating in the forward direction and
+V.sub.i when the spindle is rotating in the reverse direction).
Thus, the signal AV is converted into a coarse position deviation
signal CPD. Further, the initially set voltage ISV and a bias
signal BIS, shown in FIG. 7(a), are generated within the rotational
position deviation signal generating circuit 11a. The voltage value
V.sub.i of the voltage ISV has been set so that it is equal to a
rotational position deviation which corresponds to one revolution
(360.degree.) of the spindle when in the high gear setting.
In accordance with an orientation command signal ORCM from the
orientation command circuit 2, the speed command CV becomes either
a voltage corresponding to the speed V.sub.H at which point the
spindle stopping mode begins as shown in FIG. 1(a) for the high
gear condition, or becomes a voltage corresponding to the speed
V.sub.L at which point the spindle stopping mode begins; as shown
in FIG. 1(b) for the low gear condition. Accordingly, when the
rotational speed of the spindle 7 falls and reaches the command
speed, the signal VSR, indicating that the prescribed speed has
been reached, goes to logical "1". When this occurs, the rotational
position deviation signal generating circuit 11a generates the
initially set voltage ISV from the time that the signal VSR goes to
logical "1" until the time t.sub.2 at which the spindle initially
reaches the predetermined rotational position. The initially set
voltage ISV will, of course, differ between the low and high gear
settings. For example, it is obvious that ISV will correspond to
V.sub.H in the high gear condition and to V.sub.L in the low gear
condition. Furthermore, it will be assumed that the spindle is
rotating in the forward direction at the time that it is to be
stopped at the predetermined rotational position.
As the spindle continues to rotate and the magnetic body 10a (the
specified point on the spindle) approaches the predetermined
rotational position for the second time, the coarse position
deviation signal CPD, whose polarity will be negative, is generated
until the magnetic body 10a draws near to the area NCP (defined
between -.theta..sub.1 and +.theta..sub.1) in the environs of the
predetermined rotational position, that is, until it arrives at the
position -.theta..sub.2. Furthermore, the bias signal BIS is
generated until the above-mentioned area NCP is reached. The fine
position deviation signal DV.sub.2 is generated after the magnetic
body 10a has reached the point NCP in the environs of the
predetermined rotational position. The result of these operations
is generation of the rotational position deviation signal RPD,
whose polarity is negative, which is shown in FIG. 7(a). It should
be noted that the bias signal waveform BIS may be excluded from the
signal RPD by setting .theta..sub.2 equal to .theta..sub.1.
If the spindle is to be stopped at the predetermined rotational
position while rotating in the reverse direction, +V.sub.i is
generated as the initially set voltage signal ISV, a coarse
position deviation signal of a positive polarity is provided as the
signal CPD, and +V.sub.j is generated as the signal BIS. The result
is the bias rotational position deviation signal RPD having a
positive polarity.
The operation of the control circuit of FIG. 5 for stopping the
spindle at a predetermined rotational position, will now be
described with reference to FIGS. 5 and 7(b) for a case in which
the spindle 7 is rotating in the forward direction. It should be
noted that the rotational position deviation signal RPD in FIG.
7(b) is shown as its absolute value.
During rotation of the spindle the changeover switch 12 is
connected to the a side in FIG. 2, thereby creating a speed control
loop. More specifically, the adder 3a receives the speed command
signal CV and the actual speed signal AV from the tachometer 5, and
responds by generating a rotational speed deviation voltage. The
voltage-to-phase converter 3c controls the firing angle of the
thyristors in the thyristor converter 3d in dependence upon the
speed deviation voltage, so that the thyristor converter 3d
regulates the voltage applied to the DC motor 4. As a result, the
actual speed of the motor 4 is regulated to bring it into
coincidence with the command speed. Therefore the speed control
loop regulates the speed of the motor in order to rotate the
spindle at approximately the commanded speed.
When the machining work is completed under these conditions, a
control device, such as a numerical control device, instructs the
orientation command circuit 2 to apply the orientation command
signal ORCM to the loop changeover circuit 11b at the time t.sub.0,
shown in FIG. 2, in order to place this circuit in the set state.
At the same time, the orientation command signal ORCM is applied to
the speed command circuit 1, so that the speed command CV becomes a
voltage corresponding to V.sub.H or V.sub.L. The actual speed of
the spindle consequently decreases and follows the speed command
CV. When the actual speed coincides with the value of the speed
command, the signal VSR is generated within the position deviation
signal generating circuit 11a, and causes the loop changeover
circuit 11b to change the switch 12 from the side a to the side b,
so that circuit operation now changes from speed control to
position control. The position deviation signal generating circuit
11a first generates the initially set voltage ISV in response to
the signal VSR. As a result, the spindle continues to rotate at the
constant speed V.sub.H or V.sub.L even when the control loop is
switched over. As the magnetic body 10a continues to rotate and
reaches the predetermined rotational position for the first time
(time t.sub.2), the rotational position deviation signal generating
circuit 11a begins generating the coarse position deviation signal
CPD. As the spindle continues to rotate and the magnetic body 10a
approaches the area NCP in the environs of the predetermined
rotational position (time t.sub.3), the position deviation signal
generating circuit 11a generates the bias signal BIS. Then, when
the magnetic body 10a arrives at the above-mentioned area (time
t.sub.4), the fine position deviation signal DV.sub.2 starts being
generated. When the signal DV.sub.2 has decreased to zero, namely
when the central portion of the magnetic body (the specified point
on the spindle) is directly confronting the central portion of the
saturable reactor SRA.sub.2, the spindle stops rotating. This
completes positioning control of the spindle.
Reference will now be made to the detailed circuit diagram of FIG.
8 for a complete understanding of the principal portions of the
rotational deviation signal generating circuit 11a, and to the
associated timing chart of FIG. 9. Portions in FIG. 8 identical
with those of FIG. 2 are denoted by like reference characters and
are not described again in order to avoid prolixity.
In FIG. 8, a circuit 101 is included to generate the initially set
voltage ISV and the bias signal BIS, to integrate the actual speed
voltage signal AV, and to subtract the output voltage, resulting
from the integration operation, from the initially set voltage ISV.
Specifically, a changeover switch SW is switched over to either a
+15 volt side or a -15 volt side in accordance with the direction
of spindle rotation. If the spindle is rotating in the forward
direction, the connection is to the -15 volt side. This voltage is
divided by resistors r.sub.1, r.sub.2, and a capacitor C is charged
by an amplifier AMP.sub.1, a resistor r.sub.4 and a switch S.sub.9,
the voltage charged in the capacitor becoming the value V.sub.i of
the initially set voltage ISV. If the actual speed signal AV enters
the circuit 101 through a switch S.sub.8 or S.sub.7 after the
switch S.sub.9 has been opened, the capacitor C discharges at the
time constant RC since the voltage value of the actual speed signal
AV is lower than V.sub.i. As a result the coarse position deviation
signal CPD, generated due to the subtraction of the output voltage,
generated by integrating the actual speed signal AV, from the
initially set voltage ISV, appears at the output of the amplifier
AMP.sub.2. The amplifier AMP.sub.2, resistor R and capacitor C
comprise an integration circuit. If the switches S.sub.9, S.sub.10
are closed after the voltage of the signal CPD reaches a specified
value V.sub.j, the circuit 101 acts as an amplifier, and the bias
signal BIS at the specified level V.sub.j is generated and appears
at the output of the amplifier AMP.sub.2. In other words, in
accordance with the particular combination and timing of the
opening and closing operation of the switches S.sub.7 through
S.sub.10, first the initially set voltage ISV is generate, then the
coarse position deviation signal CPD, and finally the bias signal
BIS.
Blocks 102 and 103 of FIG. 8 denote changeover circuits for
switching gain in dependence upon gear ratio. These changeover
circuits are operable to set the positioning gain of the position
control loop high when the gears between the DC motor 4 and spindle
7 are set low. Specifically, switches S.sub.7, S.sub.2 are closed
to raise the gain when in low gear, and switches S.sub.8, S.sub.3
are closed to lower the gain when in high gear.
The gain changeover circuit 103 includes: an analog adder AAD; a
variable resistor VR.sub.1 for adjusting the gain of the adder; a
variable resistor VR.sub.2 for dividing the output voltage of the
adder AAD and for adjusting the dividing ratio; variable resistors
VR.sub.1 ' and VR.sub.2 ' for adjusting spindle stopping position;
and switches S.sub.2 and S.sub.3. Variable resistor VR.sub.1 is for
adjusting positioning gain for the low gear setting, and variable
resistor VR.sub.2 is for adjusting positioning gain for the high
gear setting. The variable resistors VR.sub.1 ' and VR.sub.2 ' are
employed when adjusting the stopping position of the spindle. More
specifically, there are instances where the stopping position
shifts because of a change in the constant deviation caused by
varying the positioning gain in accordance with the high gear/low
gear condition. The variable resistors VR.sub.1 ' and VR.sub.2 '
are included in order to correct for this shift in stopping
position. In accordance with the above arrangement, changing over
the gain by means of the changeover circuits 102 and 103 permits
the amplitude of the rotational speed deviation voltage RPD,
obtained from the output terminal OUT, to be made several times
larger in low gear than the amplitude of RPD when in high gear.
Thus, it is possible to raise the rotational speed of the spindle
motor when in low gear and thus reduce the time required for the
spindle positioning control operation.
Block 104 of FIG. 8 is a well-known absolute value circuit which
generates the absolute value of the output from the circuit 101. A
comparator 105 detects whether or not the coarse position deviation
signal CPD has fallen below a predetermined level, and generates a
signal NRPS which indicates that the predetermined portion (the
magnetic body 10a) has drawn near the area NCP in the environs of
the predetermined rotational stopping position. The signal NRPS
closes the switches S.sub.9, S.sub.10.
A gain adjustment circuit 106 adjusts the gain in dependence upon
the gap between the magnetic body 10a and the sensing portion 10b,
and generates the detection voltage DV.sub.2 (the fine position
deviation voltage) having a prescribed slope. A slicer circuit 107
slices the approach signal ASV at a predetermined level and
generates a signal LS which indicates that the magnetic body has
reached the area NCP in the environs of the predetermined
rotational position. The signal LS opens the switches S.sub.5,
S.sub.6 and closes switch S.sub.4. As a result, the fine position
deviation signal DV.sub.2 is delivered as the deviation signal.
A forward-reverse changeover circuit 108 has a switch S.sub.5
closed when the spindle is controlled by rotating it in the forward
direction, and a switch S.sub.6 closed when the spindle is
controlled by rotating it in the reverse direction. An
"in-position" signal generating circuit 109, comprising a
comparator, monitors the fine position deviation signal DV.sub.2
and generates the in-position signal INPOS when the spindle is
within range of the predetermined rotational position. Thereafter a
signal indicating completion of the orientation operation is
transmitted to the numerical control unit.
Comparators 110 and 111 of FIG. 800 monitor the fine position
deviation signal DV.sub.2 and generate signals NEG and POS,
respectively upon detecting whether the spindle is approaching the
predetermined rotational direction while rotating in the reverse
direction (signal NEG at logical "1") or while rotating in the
forward direction (signal POS at logical "1"), respectively. One of
the switches S.sub.5 or S.sub.6 will be closed and the other switch
will be opened by the signals VSR and LS depending upon which of
the signals NEG or POS is a "1". The analog adder AAD of the gain
changeover circuit 103 generates either the fine position deviation
signal or the coarse position deviation signal in accordance with
the open or closed state of the switches S.sub.4, S.sub.5 or
S.sub.6. A speed detection circuit 113 receives the voltage AV
indicative of the actual speed of the spindle and, in the high or
low gear condition, generates the signal VSR when the actual speed
reaches the prescribed speed, and generates a zero speed signal VZR
when the actual speed reaches zero. An orientation completion
signal generating circuit 114 receives the in-position signal
INPOS, the zero speed signal VZR, and the orientation command
signal ORCM, and takes the logical product of these signals. In
other words, the orientation completion signal ORDEN is generated
when INPOS, VZR and ORCM are all at logical "1".
In summary, if the orientation command signal ORCM goes to logical
"1" at time t.sub.0, the voltage indicative of the command speed CV
decreases, and so does the actual speed AV, with AV becoming
V.sub.i at time t.sub.1. At this time the signal VSR, indicative of
the fact that the specified speed has been reached, goes to logical
"1", switch 12 is switched, one of the switches S.sub.2 or S.sub.3
is closed in accordance with the low/high setting of the gears, and
one of the switches S.sub.5, S.sub.6 is closed in accordance with
the direction, either forward or reverse, of spindle rotation. This
forms a position control loop, with the initially set voltage ISV
(=V.sub.i) being output by the changeover switch 12 when in high
gear, and K.multidot.V.sub.i (K>1) being generated when in the
case of low gear. (It should be noted that switch S.sub.9 is
closed, and that switches S.sub.7, S.sub.8, S.sub.10 are open).
As a result, the DC motor continues rotating at a constant speed
corresponding to V.sub.i or to K.multidot.V.sub.i and the spindle
reaches the predetermined rotational position the first time (i.e.,
the signal LS is a "1", and the signal INPOS is a "1"). Hence, at
time t.sub.2, switch S.sub.9 is opened and one of the switches
S.sub.7, S.sub.8 is closed in dependence upon the low/high setting
of the gears. Therefore the coarse position deviation signal CPD is
output by the changeover switch 12. Thereafter, as the actual speed
and the position deviation decrease and the spindle approaches a
point in the environs of the predetermined rotational position
(time t.sub.3), the comparator 105 generates the signal NRPS
(logical "1), causing the switches S.sub.9, S.sub.10 to be closed.
As a result, the bias signal BIS at the prescribed level is output
by the changeover switch 12. As the spindle continues to rotate at
the slower speed and reaches the area NCP in the environs of the
predetermined rotational position (time t.sub.4), the signal LS
goes to the "1" level, switches S.sub.5, S.sub.6 are opened, and
switch S.sub.4 is closed. Hence, the fine position deviation signal
DV.sub.2 is output by the changeover switch 12. When the magnetic
body 10a (the predetermined point on the spindle) comes within
range of the predetermined rotational position, the in-position
signal INPOS is generated. This is followed by the actual speed of
the spindle falling to zero, whereupon the zero speed signal VZR
goes to logical "1". This completes the control operation for
stopping the spindle at the predetermined rotational position, the
orientation completion signal ORDEN being generated by the
orientation completion signal generating circuit 114.
It should be noted that overshooting and hunting occur when the
positioning gain exceeds a threshold value in the vicinity of the
command value. This will be explained with reference to FIG.
10.
The shaded portion in FIG. 10 represents a threshold region within
which overshooting does not occur. The solid line represents a case
in which the positioning gain exceeds the threshold in the vicinity
of the command value, and the broken line represents a case in
which the positioning gain does not exceed the threshold in the
vicinity of the command value. Overshooting occurs in the former
case but not in the latter. It follows then that the foregoing
should be considered when setting the positioning gain.
In accordance with the present invention as described above, the
positioning gain can be held constant regardless of the high or low
gear setting, thereby allowing a marked reduction in the time
needed to achieve positioning of the spindle at the predetermined
location under a low gear condition. This in turn permits an
increase in the proportion of time actually used for machining, so
that working efficiency can be enhanced.
While the present invention has been described for a case in which
gears are employed as the speed change mechanism, it is obvious
that the invention can be applied to a clutch-type speed changer or
the like. Moreover, the position sensor described above is not
limited to the magnetic sensor. Suitable position sensors include
position coders, resolvers and the like.
Although the present invention has been described in its preferred
form with a certain degree of particularity, it is obvious that
many modifications and variations are possible in light of the
above teachings. It is therefore to be understood that within the
scope of the appended claims, the invention may be practiced
otherwise than as specifically described.
* * * * *